1. Field of the Invention
The present invention relates to a toner used for a recording method, such as an electrophotographic method, an electrostatic recording method, and a toner jet type recording method. In particular, the present invention relates to a toner used for a copying machine, a printer, or a facsimile, each of which forms a fixed image in such a way that a toner image formed on an electrostatic latent image carrier is transferred onto a transfer member and is then fixed under heat pressure conditions.
2. Description of the Related Art
In recent years, energy saving has been considered as a significant technical subject also in electrophotographic apparatuses, and a substantial reduction in heat quantity consumed for a fixing device has been discussed. Accordingly, a toner has been required to be fixed by lower energy.
Heretofore, in order to perform fixing at a lower temperature, a method which enables a binder resin to have a sharper melt property has been known as one of effective methods. From this point of view, a toner using a crystalline polyester resin has been introduced. Since molecular chains of a crystalline polyester resin are regularly aligned, the crystalline polyester resin has not a clear glass transition temperature and is not likely to be softened up to its crystalline melting point. Accordingly, attention has been paid to the crystalline polyester resin as a material which is able to satisfy heat-resistant storage stability and low-temperature fixability at the same time. However, although the crystalline polyester resin itself has a sharp melt property, the elasticity thereof at a high temperature is not enough, and there has been a problem in that high-temperature offset is liable to occur. Therefore, in general, the use of the crystalline polyester in combination with an amorphous polyester has been studied.
Japanese Patent Laid-Open No. 2004-191927 has disclosed that as a toner using a crystalline polyester for a binder resin, in a capsule type toner containing a crystalline polyester and an amorphous polymer, the storage elastic modulus and loss modulus at a temperature of its melting point +20° C. are controlled to improve the fixing latitude.
Japanese Patent Laid-Open No. 2007-114635 has disclosed that by using a block copolymer obtained by esterification of a crystalline polyester block and an amorphous polyester block, fixing can be performed by low-temperature heating.
Japanese Patent Laid-Open No. 2008-052192 has disclosed a toner having improved heat-resistant storage stability and high-temperature offset resistance by a urea-modified polyester formed by bonding a segment of a crystalline polyester and a segment of an amorphous polyester with an amino cross-linking agent.
However, it was found that since the toner disclosed in Japanese Patent Laid-Open No. 2004-191927 is used by mixing the crystalline polyester and the amorphous polymer, the elasticity at a high temperature is not sufficient, a decrease in glossiness is liable to occur due to infiltration of the toner into paper, and the temperature range for fixing is decreased by the high-temperature offset.
In addition, since the toners disclosed in Japanese Patent Laid-Open Nos. 2007-114635 and 2008-052192 each uses the block polymer formed by binding an amorphous polyester and a crystalline polyester, the viscosity at a high temperature can be adjusted by the amorphous polyester, and hence the high-temperature offset can be suppressed. However, in the toners described above, the content of the crystalline polyester in the total binder resin is low, and in addition since an endothermic peak derived from the crystalline polyester detected by a differential scanning calorimeter (DSC) measurement is considerably broad, it was found that the crystallinity thereof is low.
The reason for this is believed that since these toners are each formed through a heating step at the melting point or more of the crystalline polyester in a manufacturing process, the crystallinity thereof is degraded due to the thermal history described above. As a result, the intrinsic sharp melt effect of the crystalline polyester cannot be fully obtained, and the effect of low-temperature fixability is not enough.
As described above, even when these crystalline polyesters are used, it is difficult to obtain a toner having a wide fixing temperature region from a low temperature to a high temperature, and hence a toner having further improved properties has been desired.